Field
The disclosed concept pertains generally to microgrid systems, and, more particularly, to a multi-source microgrid system that includes one or more distribution manager having a number of smart circuit breakers wherein the trip curves of the circuit breakers can be dynamically adjusted based upon the available source overcurrent in a given direction that may be provided to (i.e., sourced through) a circuit breaker (and optionally on other criteria such as, without limitation, total available source overcurrent to a given conductor, size of the buss bar or interconnection cable, type of source or type/criticality of load).
Background Information
A distributed power source is a secondary power generation mechanism other than the primary utility feed used to provide an alternative to or an enhancement of the traditional electric power system. Distributed power sources include, for example and without limitation, photovoltaic (PV) systems, wind turbines, backup generators, energy storage, and uninterruptible power supplies.
A microgrid is a discrete energy system consisting of a number of distributed energy sources and loads capable of operating in parallel with, or independently from, the main grid. When connected to the main grid, a microgrid will rely on a mix of power generation sources depending on the metric to be optimized (cost, greenhouse gas emissions, reliability). In the case where the microgrid is operating independently from the main grid (e.g., when the point of common coupling with the main grid has been disconnected), the microgrid is typically said to be operating in an islanded mode.
Microgrids are desirable as the multiple dispersed generation sources of a microgrid and the ability to isolate the microgrid from a larger network generally provide highly reliable electric power. Typically, specialized hardware and software systems control the integration and management of the components of a microgrid and the connection to the main grid.
Circuit protection in microgrid type systems where multiple, current limited sources are feeding into a shared/common bus, and where multiple loads may be present (or added over time) could cause an overcurrent condition to occur where the sources cannot deliver adequate power to support the loads. Circuit breaker trip curves today are manually (statically) set to match the source or load they are protecting. However, when sources and loads change over time within a microgrid, it is necessary to dynamically adjust the trip curve to match the available source overcurrent from the source(s). As new sources or loads are plugged in or added over time at any power port on a microgrid system, there is the potential for overload currents to become present on the common bus. This is of particular concern for a power distribution topology that may evolve/change over time and allows for bidirectional power flow. Different policies or strategies based on different operating conditions and scenarios can also be performed with dynamically adjustable trip curves.